1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic storage apparatus based on the use of the same. In particular, the present invention relates to a magnetic recording medium which is usable to record a large amount of information quickly and correctly and reproduce recorded information at a low noise level. The present invention also relates to a method for producing the same and a magnetic storage apparatus based on the use of the same.
2. Description of the Related Art
In recent years, in response to the development of advanced information society, the needs increasingly expand for the realization of the large capacity and the high density of the information recording apparatus. The magnetic storage apparatus is known as one of information recording apparatuses which respond to such needs. The magnetic storage apparatus is used, for example, as the large capacity storage apparatus, for example, for large scale servers, parallel computers, personal computers, network servers, movie servers, and mobile PC's. The magnetic recording apparatus is provided with a magnetic recording medium on which information is recorded, and a magnetic head which is used to record and reproduce information on the magnetic recording medium. The magnetic recording medium includes a ferromagnetic thin film composed of cobalt alloy or the like which is formed as a recording layer on a disk-shaped substrate, for example, by means of the sputtering method. A protective layer and a lubricating film are formed on the recording layer in order to enhance the sliding resistance and the corrosion resistance.
As the magnetic recording apparatus has a large capacity, the improvement in recording density is advanced for the magnetic recording medium by recording minute recording magnetic domains in the recording layer of the magnetic recording medium. The perpendicular magnetic recording system attracts attention as a method for minutely recording the recording magnetic domains. In the perpendicular magnetic recording system, the magnetic recording is performed by forming magnetic domains having perpendicular magnetism in a recording layer by using a magnetic recording medium having the recording layer which exhibits the perpendicular magnetism. In the perpendicular magnetic recording system as described above, the minute magnetic domains can be formed in the recording layer, and hence the recording density of the magnetic recording medium can be increased.
A polycrystalline film based on the Co—Cr system has been hitherto used as a material for the recording layer of the magnetic recording medium which conforms to the perpendicular magnetic recording system as described above. The polycrystalline film has a structure in which the ferromagnetic Co-rich areas and the non-magnetic Cr-rich areas are separated from each other, and the non-magnetic area interrupts the magnetic interaction which would otherwise act between the adjoining ferromagnetic areas.
In order to further improve the areal recording density of the magnetic recording medium, it is necessary to reduce the medium noise. For this purpose, it is known to be effective that the unit of inversion of magnetization is made fine and minute and the reading head is supersensitized. Especially, in order to make the unit of inversion of magnetization to be fine and minute, it is known to be effective that the magnetic crystal grains are made fine and minute. However, if the magnetic crystal grains are made excessively fine and minute, the so-called thermal demagnetization is consequently caused, in which the state of magnetization of the magnetic crystal grains is thermally unstable. In order to avoid such an inconvenience, for example, Japanese Patent Application Laid-open No. 8-30951 discloses a magnetic recording medium comprising a soft magnetic layer, a first seed layer composed of carbon, a second seed layer, and a recording film having an artificial lattice structure which are successively stacked on a non-magnetic substrate in this order.
The artificial lattice multilayer film and the superlattice alloy film have high magnetic anisotropy. Therefore, a high resistance is expected with respect to the thermal disturbance. However, these films have such a drawback that small magnetic domains cannot be formed and the transitional medium noise is large, because the magnetic interaction is intensive in the in-plane direction (direction parallel to the substrate surface) unlike the polycrystalline film based on the Co—Cr system. In the magnetic recording medium disclosed in Japanese Patent Application Laid-open No. 8-30951 described above, the second seed layer composed of Pt or Pd is provided on the first seed layer composed of carbon formed on the soft magnetic layer, and the artificial lattice layer of Co/Pt or Co/Pd is formed thereon. Accordingly, the crystalline orientation of the artificial lattice layer is improved, the perpendicular magnetic anisotropy is enhanced, and the coercivity is improved. However, in the case of such a magnetic recording medium, the magnetic exchange coupling force in the in-plane direction of the recording layer is intensified, and the transition noise, which appears as the jitter when the track recording density is increased, becomes high. As a result, it is difficult to perform recording and reproduction at a high recording density. Further, the following problem arises. That is, the writing magnetic field from the magnetic head does not effectively arrive at the soft magnetic layer, and the saturation recording characteristics are inferior, because the two seed layers, i.e., the first seed layer and the second seed layer are used.
In the 24th Annual Conference on Magnetics in Japan (2000) held by Magnetics Society of Japan, Omori et al. disclose a magnetic recording medium which uses Au—SiO2 and PdB—O as a seed layer on a substrate and which uses an artificial lattice layer composed of CoB—O layers and PdB—O layers as a recording layer.
In AIT-MINT Workshop 2001, Jack H. Judy et al. disclose a magnetic recording medium which uses ITO (Indium-Tin-Oxide)/Pd as a seed layer and which uses an artificial lattice layer composed of CoB layers and Pd layers as a recording layer.